WASHINGTON — First the U.S. government temporarily banned laptops in the cabins of some airplanes. Now it is looking to ban them from checked luggage on international flights, citing the risk of potentially catastrophic fires.

The Federal Aviation Administration recently recommended that the U.N. agency that sets global aviation standards prohibit passengers from putting laptops and other large personal electronic devices in their checked bags.

The FAA says in a filing with the International Civil Aviation Organization that the lithium-ion batteries in laptops can overheat and create fires.

Some questions and answers about the shifting U.S. policy.

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WHY IS THE FAA WORRIED ABOUT THIS DANGER NOW?

The FAA has long been concerned about the potential hazardous of lithium batteries. The agency’s tests of the risks of shipping large quantities of batteries as cargo on airliners showed that when a single battery overheats, it can cause other nearby batteries to overheat as well. That can result in intense fires and the release of explosive gases.

Based on those test results, the FAA was able to convince ICAO two years ago to ban cargo shipments of lithium batteries on passenger planes and to require that batteries shipped on cargo planes be charged no more than 30 per cent. The risk of overheating is lower if the battery isn’t fully charged.

More recently, the FAA conducted 10 tests of fully charged laptops packed in suitcases. In one test, an 8-ounce aerosol can of dry shampoo –which is permitted in checked baggage — was strapped to the laptop. A heater was placed against the laptop’s battery to force it into “thermal runaway,” a condition in which the battery’s temperature continually rises. There was a fire almost immediately and an explosion within 40 seconds with enough force to potentially disable the fire suppression system.

Other tests of laptop batteries packed in suitcases with goods like nail polish remover, hand sanitizer and rubbing alcohol also resulted in large fires, although no explosions.

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ISN’T THE GOVERNMENT CONTRADICTING ITSELF BY FIRST SAY LAPTOPS SHOULD BE CHECKED, THEN SAYING THEY SHOULDN’T?

The different messages are the result of two agencies with different missions: security versus safety.

Last March, the Department of Homeland Security imposed a ban on laptops in the cabins of planes coming into the U.S. from 10 Middle Eastern airports to prevent them from being used as a tool in an attack. Many passengers put their laptops in their checked bags instead. The ban was fully lifted in July after airports in the region took steps to improve security.

This ban is being sought by the FAA, which is focused on the risk of an accidental explosion more than the prospect of a terrorist attack.

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WHEN WILL THIS GO INTO EFFECT?

There are no guarantees that there will be ban on packing laptops in checked bags.

The FAA is presenting its case at a meeting this week and next of ICAO’s dangerous goods panel. European aviation safety regulators, aircraft manufacturers and pilots’ unions have endorsed the proposal.

Even if the panel were to agree with the proposal, it would still need to be adopted at higher levels of ICAO. And it would only apply to international flights.

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WILL THE U.S. IMPOSE A BAN ON CHECKING LAPTOPS ON DOMESTIC FLIGHTS?

This is unclear. Individual countries can decide whether to implement domestic bans. The United States has not indicated if it will do so.

The effect of such a ban may not be great, since many passengers don’t check bags to avoid surcharges, and those that do often prefer to carry on electronics.

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WILL THE U.S. CONTINUE TO PUSH FOR THE INTERNATIONAL BAN?

This is also unclear. The FAA, which favours the ban, is handling negotiations for the U.S. at the ICAO meeting. But, for future meetings, Transportation Secretary Elaine Chao is having another agency, the Pipeline and Hazardous Materials Safety Administration, take the lead.

It’s not clear if that agency, known as PHMSA, will share the FAA’s position.

PHMSA previously led dangerous goods negotiations, but the Obama administration put the FAA in charge after congressional Democrats complained that PHMSA officials were too cozy with the industries they regulated.

The Transportation Department said in a statement that PHMSA “has a unique and highly effective” approach to regulating the transportation of hazardous materials, and that it will consider what impact any change in aviation rules might have on transportation. The statement also said PHMSA will collaborate with the FAA.